JPH02305073A - Image pickup device - Google Patents

Abstract

PURPOSE:To obtain an excellent image whose shadow parts have no deficiency of gradations due to back light by controlling a stop means according to the output signal of a pattern decision means and a video signal obtained by an image pickup means. CONSTITUTION:The pattern decision means 101 decides whether a subject in a back light state or not and when the back light state is detected, a stop control means 102 controls the stop means 2 so that the influence of the large- level signal of the video signal is eliminated, thereby correcting the back light. Thus, this device is provided with a correcting function which decides the state of the back light, etc., wherein a light-dark ratio is large and performs control for opening the stop to correct the darkening of a desired subject, so the excellent image whose shadow part has no deficiency of gradations due to back light is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an imaging apparatus having an automatic aperture circuit that performs effective aperture correction when capturing an image with a large contrast ratio such as backlight.

2. Description of the Related Art Aperture correction in conventional imaging apparatuses has been performed using a method that is a mixture of a peak value method and an average value method.

FIG. 12 shows a block diagram of this conventional imaging device, in which 1 is a lens, 2 is an aperture, 3 is an imaging device such as a CCD, and 4 is a device that amplifies the signal from the imaging device 3 to capture an image at a predetermined level. an amplifier circuit for obtaining a signal; 6 a signal processing circuit that performs gamma processing; 120 a peak level detection circuit that detects the peak level of the image signal; 121 an average level detection circuit that detects the average level of the image signal; is an aperture drive circuit that drives the aperture.

In the conventional imaging device configured as described above, the aperture drive circuit 12 controls the aperture so that a signal obtained by mixing the output signal of the peak level detection circuit 120 and the output signal of the average level detection circuit 121 becomes equal to the reference. It was driving 2.

Problems to be Solved by the Invention However, with the above-mentioned conventional configuration, when backlit imaging or when imaging an object with a large contrast ratio including a light source, the aperture is closed by the output signal of the peak level detection circuit 120, and the desired image cannot be captured. This has the problem that the subject becomes dark and submerged.

SUMMARY OF THE INVENTION An object of the present invention is to provide an imaging device having a correction function that corrects for darkening of a subject by determining conditions such as backlight where the ratio of brightness to darkness is large and controlling the opening of the aperture.

Means for Solving the Problems The present invention provides an imaging means for converting a subject image into an electrical signal;
an aperture means for limiting the amount of light incident on the imaging means; a pattern discrimination means for classifying a subject image into patterns from a video signal obtained from the imaging means; an output signal of the pattern discrimination means and a video signal obtained from the imaging means; and an aperture control means for controlling the aperture means according to the image pickup apparatus.

Operation With the above configuration, the pattern discrimination means determines whether the subject is in a backlit condition, and when a backlit condition is detected, the aperture control means adjusts the aperture so that it will not be affected by a signal with a high level of video signal. Backlighting is corrected by controlling the means.

Embodiment FIG. 1 shows a block diagram of an imaging apparatus of the present invention. In FIG. 1, the same components as those in the conventional example shown in FIG. 12 are given the same reference numerals, and their explanations will be omitted.

In the figure, 101 is a pattern discrimination circuit that discriminates the state of the subject, and 102 is an aperture control circuit that inputs the output signal of the pattern discrimination circuit 101 and a video signal to control the aperture 2.

Regarding the imaging device of this embodiment configured as described above,
The operation will be explained below.

FIG. 2 is a diagram showing the configuration of the pattern discrimination circuit 101 shown in FIG. 1. In FIG. 2, 20 is the amplifier circuit 4 of FIG.
This is a terminal for inputting video signals from. 21 is a standard level detection circuit (output is L) for detecting the average level of the video signal, and 22 is a peak level detection circuit (output is PEAK) for detecting the peak level of the video signal. 2
3 is a standard level detection circuit 21 and a peak level detection circuit 2
This is a pattern determination circuit that outputs a signal corresponding to the output signal of No. 2, and its output is inputted to the aperture control circuit 102 of FIG. 1 through a terminal 24.

FIG. 3 is a diagram for explaining the operation of the pattern determination circuit 23. In the figure, the horizontal axis is the standard level detection circuit 2.
1 is output, and the vertical axis is the output PEAK of the peak level detection circuit 22. The broken line a in the figure shows the relationship between L and PEAK when photographing a backlit subject with a light source in the background, and b indicates the relationship between L and PEAK when photographing a subject in normal order.
It shows the relationship between AK.

In general, the peak level is large for a backlit subject, so PEAK at any L is always larger than in the case of a frontlit subject. Therefore, it is possible to divide the relationship between L and PEAK into two areas, A and B, using the boundary indicated by a solid line, and determine whether the subject is backlit based on which area, A or B, the subject falls into. .

FIG. 4 is a diagram showing the characteristics of the pattern determination circuit 23.

In this figure, the horizontal axis is the line indicated by x1 in FIG. 3, and the direction of the arrow indicates the direction from area B to area A in FIG. 3. The vertical axis is the output of the pattern determination circuit 23, and its value is set as n. The pattern determination circuit 23 outputs n=1.0 if the subject is within area B, and outputs n=0.0 if the subject is within area A. Intersection of area B and area A (■)
Nearby, the value changes gradually from n=1.0 to n=0.0.

FIG. 5 is a block diagram showing the configuration of the aperture control circuit 102 in FIG. 1. In the figure, a terminal 50 is connected to the amplifier circuit 4 of FIG. 51 is an average level detection circuit (output is A) for detecting the average level of the video signal;
2 is a peak level detection circuit (output is B) that detects the peak level of the video signal. 53 is a mixing circuit (output is set to V) that mixes the outputs of the average level detection circuit 51 and the peak level detection circuit 52 according to the signal of the output of the pattern discrimination circuit 101 (input from the terminal 54);
is an aperture drive circuit that drives the aperture 2 so that the output of the mixing circuit 53 and the reference become equal.

The output V of the mixing circuit 53 is VIA X n +P X (1-n) 0.
It is determined by 0≦n≦1.0. When the pattern discrimination circuit 101 discriminates that the subject is the next subject, it outputs fi=0.0. Therefore, the output V of the mixing circuit 53 becomes v=P, and the aperture is controlled at the peak level of the video signal, making it possible to control the aperture without causing signal saturation.

On the other hand, when the pattern discrimination circuit 101 discriminates that the subject is backlit, it outputs n=1.0. Therefore, the output V of the mixing circuit 53 becomes the VIA, and the aperture is controlled based on the average level of the video signal, making it possible to reduce the influence of the light source.

As described above, according to this embodiment, the pattern discrimination circuit 101
By discriminating the state of the subject and optimally controlling the aperture depending on the backlight and sequential conditions, it is possible to obtain a good image without crushed shadows due to backlight.

Note that the average level detection circuit 51 and the peak level detection circuit 52 in FIG. 5 are used to reduce the influence of the light source and to prevent signal saturation, respectively, and any circuit that can achieve the same functions may be used. It is not limited to this.

Next, a second configuration example of the pattern discrimination circuit 101 of the present invention will be described below.

FIG. 7 shows a second embodiment of the pattern discrimination circuit 101.

In FIG. 2, the outputs of the standard level detection circuit 21 and the peak level detection circuit 22 are used to discriminate between a backlit subject including a light source and a frontlit subject. However, the standard level detection circuit 21
Even if the output of the peak level detection circuit 22 and the output of the peak level detection circuit 22 are the same, there are objects in different states. For example, even if the output of the peak level detection circuit 21 is the same, the proportion of the bright portion to the entire screen varies. When a bright portion occupies a large proportion of the entire screen, it is often desirable to control the aperture so that the bright portion is at an appropriate level.

In this configuration, the bright part of the screen indicated by 70 (
An intermediate level detection circuit is newly installed to detect the signal level (the remaining 20% of the entire screen) excluding dark areas (for example, 60% of the entire screen) and dark areas (20% of the entire screen, as an example). By using the output signal for pattern determination, more fine-grained aperture control is achieved. 71 is a pattern determination circuit. Below, Figures 6 and 8.

The explanation will be given based on FIGS. 9, 10, and 11.

FIG. 6 shows the signal level of the object for one horizontal scanning period. In the same figure, the standard level detection circuit 21
and the output of the peak level detection circuit 22 to PE.
AK indicates the output of the intermediate level detection circuit 70.

Figure 6(a) shows a backlit subject including a light source, etc.
Figure (C) shows a front-lit subject. FIG. 6(b) and FIG. 6(d) are subjects whose PEAK level is the same, but the proportions of the bright parts of the screen are different. In this embodiment, since the proportion of bright areas on the screen is small in FIG. 6(b), aperture control is performed so that it is not affected by bright areas.
In FIG. 6(d), since the ratio of the bright parts of the screen is large, the aperture is controlled so that the bright parts have an appropriate level.

The operation of the pattern determination circuit 71 will be explained below.

FIG. 8 is a diagram showing the relationship between PEAK and PEAK obtained in the same manner as in FIG. The broken lines indicated by FLv by C+ d in the figure are (a), (b), (c),
It shows the relationship between L and PEAK when a subject corresponding to (d) is photographed.

The pattern determination circuit 71 divides FIG. 8 into three regions C, D, and E shown by solid lines, and determines which region the subject is included in. Figure 9 is on the line indicated by X2 in Figure 8,
Indicates the characteristics for determining which area the subject is included in.

The vertical axis is a coefficient (
(denoted by K) (maximum 1.0). The coefficient indicating that it is included in area E is E (PEAK,
L), and the coefficient indicating that it is included in the area is D (PEAK, L) shown by a solid line.

FIG. 10 is a diagram showing the relationship between L obtained in the same manner as FIG. 8 and the old one. The pattern determination circuit 71 divides FIG. 10 into three areas F, G, and H shown by solid lines, and determines which area the subject is included in.

FIG. 11 shows characteristics for determining in which region the subject is included on the line indicated by X3 in FIG. 10.

The coefficient indicating that it is included in region G is G (old, L) shown by a solid line. The pattern determination circuit 71 has the above-mentioned
E (PEAK, L), D (PEAKXL)
, G(MID, L), calculate n using the following formula and output.

n = M A X (E (PEAK, L), M
I N [D (PEAK, L L G (old, L)) From the above formula, it is clear that the subject in area E in Figure 8 and the object that belongs to area G in Figure 8 and are in area G in Figure 10. It is possible to perform aperture control so that the subject to which it belongs is less affected by the light source.

As described above, according to this embodiment, the intermediate level detection circuit 7
By providing 0, it is possible to achieve fine-grained aperture control that also takes into account the proportion of bright areas on the screen, and to obtain even better images.

Note that although the standard level detection circuit 21 shown in FIG. 2 detects the average level of the video signal, this is just one example, and the present invention is not limited to this. For example, it is also possible to detect the average level of a relatively dark portion of the screen, as in the intermediate level detection circuit 70 shown in FIG. Furthermore, the standard level detection circuit 21 shown in FIG. 7 is not limited to this. For example, the signal level of a relatively bright part (remaining 20% of the entire screen) excluding the bright part of the screen (20% of the entire screen as an example) and the dark part (60% of the entire screen as an example). May be detected. Furthermore, the area division and pattern determination circuit 23 shown in FIGS. 3, 8, and 10. The characteristics of -71 are determined through experiments based on the characteristics of the image sensor, the design philosophy of the designer, etc., and are not limited thereto.

The aperture control circuit 102 shown in FIG. 5 is limited to this type of circuit as long as it can switch between control that slightly opens the aperture and control that prevents signal saturation depending on the output of the pattern discrimination circuit 101. do not have.

As described in detail, according to the present invention, by performing optimal aperture control depending on the condition of the subject, a good image without crushed shadows due to backlighting can be obtained, and its practical effects are great.

[Brief explanation of drawings]

FIG. 1 is a professional diagram of the imaging device according to the present invention, and FIG.
FIG. 3 is a diagram showing the configuration of the first embodiment of the pattern discrimination circuit 101, FIG. 3 is an explanatory diagram of the pattern discrimination circuit 23, and FIG. FIG. 8 is a configuration diagram of the second embodiment. 9, 10, and 11 are explanatory diagrams of the pattern determination circuit 71, and FIG. 12 is a block diagram of a conventional imaging device. 281. Aperture, 381. Imaging device, 419. Amplification circuit, 101, Pattern discrimination circuit, 102
,,,Aperture control circuit. Name of agent: Patent attorney Shigegami Awano et al. 18th 2nd
Figure 3: Happy 4 Figure 6: TI! J Figure 10 Figure 11■ ■ 111 (=:) Group

Claims (2)

[Claims] (1) an imaging means for converting a subject image into an electrical signal; an aperture means for limiting the amount of light incident on the imaging means; a pattern discrimination means for determining the state of the subject from a video signal obtained from the imaging means; An imaging apparatus comprising: an aperture control means for controlling the aperture means in accordance with an output signal of the pattern discrimination means and a video signal obtained from the imaging means. (2) The pattern determination means is comprised of a plurality of level detection circuits including a peak level detection circuit, and a pattern determination circuit that outputs a predetermined value corresponding to the outputs of the plurality of level detection circuits. The imaging device according to claim 1, characterized in that: